This invention relates generally to dynamoelectric machines and more specifically to an improved rotor construction for a dynamoelectric machine which helps facilitate magnetic exitation of the rotor.
Inductor type dynamoelectric machines have been employed, in the past, to achieve high speed operation, particularly for electrical generation. These machines are generally characterized by a stator which includes both AC armature and DC exitation windings, surrounding a rotor. The rotor is winding-less thereby eliminating the need for rotating field or armature coils. Accordingly, slip rings, brushes and associated connections common to machines having rotating windings are entirely eliminated. The coil-less rotor allows the dynamoelectric inductor machine to achieve high rotational speeds. The rotor is homopolar and requires magnetic excitation from the DC exitation windings to create a magnetic field which rotates the rotor.
One typical version of an inductor type dynamoelectric machine, employs a circumferentially distributed arrangement of C-shaped (sometimes referred to as "U-shaped") armature elements which surround a generally cylindrical DC exitation or field coil which in turn encloses a transverse pole magnetic rotor. U.S. Pat. Nos. 5,219,097 and 3,912,958 describe machines of this general design. These machines typically employ frame mounted hardware for directly supporting the individual components of the stator but exhibit deficiencies inherent with this construction.
A more recent version of an inductor type dynamoelectric machine is disclosed in commonly owned, U.S. Pat. No. 4,786,834, issued Nov. 22, 1988 in the name of James J. Grant, et al. As disclosed therein, a spool-like support structure for supporting the field winding and armature elements from inside and for accurately positioning armature elements provides for a more stable machine particularly at high rotational speeds. The spool-like structures which are made of a non-magnetic material have a hollow, elongated central portion extending concentrically about a longitudinal axis. This central portion supports a DC field winding and defines an interior longitudinal passageway for accommodating the insertion of a coaxial rotor. At each end of the central portion, end portions extend radially outward therefrom. Each of these end portions is preferably provided with radially oriented grooves in its axially outermost surface. The grooves are configured to receive and orient legs of the C-shaped armature core elements arrayed in a circumferentially distributed pattern about the periphery of the spool-like structure. The end portions of the spool-like structure are axially spaced and radially dimensioned having grooves in the outer face of each end portion which are angularly spaced so as to precisely position the armature elements in three orthogonal directions.
Other features, aspects, advantages and benefits of this dynamoelectric machine are detailed in U.S. Pat. No. 4,786,834, the disclosure of which is incorporated herein by reference. This particular dynamoelectric machine requires the use of DC field windings to generate a magnetic field therethrough and through the homopolar rotor to facilitate rotation of the rotor. Therefore DC power to create this magnetic field must be supplied to the field windings. The field windings comprise a helically wound conductive wire which forms a coil that surrounds the rotor. Because of the volume occupied by the field windings, access to the rotor for cooling is limited. Moreover, due to the production of DC current through the windings, heat is actually created within the windings due to the resistivity of the windings. Because the magnetic field is created by the DC windings, the magnetic flux is dictated by the number of windings within the exitation coil. However, the length of the DC exitation coil also dictates the length of the C-shaped armature element and therefore the overall length of the rotor and dynamoelectric machine.
It is therefore an object of the present invention to achieve a dynamoelectric machine which eliminates the need for DC current to be supplied thereto.
It is also an object of the present invention to achieve a dynamoelectric machine which is capable of providing magnetic exitation to the rotor without the use of field windings or exitation coils.
It is also an object of the present invention to achieve a dynamoelectric machine which contains a structure that facilitates improved cooling.
It is also an object of the present invention to provide a rotor construction which is mechanically strong and stable and may be easily manufactured.
It is also an object of the present invention to provide a dynamoelectric machine construction which facilitates the use of shorter C-shaped armature elements thereby enabling the overall length of the dynamoelectric machine to be shorter.